You can make a #1 pottery plaster mold to create a silicone positive. The positive once cured gets to be used for a coddle pour of #1 pottery plaster and 200 mesh silica to make make an investment mold that can endure the heat of the kiln. if you have many test tiles to make using silicone positives really reduce the time spent to make simple test tiles of varying color degrees. While my tiles are thin I can vary colors concentrations to allow for high and low lights to the work. In the early 2000’s at a BeCon conference Jim Jones was the sales director doing a demo of frit tinting. As a pate de verre artist I was captivated by the concept. While the demo was a single color the idea can accommodate custom blends of your choosing and allows for creative variations to support the artistic need. As usual Bullseye empowers artist to springboard ideas and use their imaginations to tweak and provide artists a lot of artistic freedom. Here’s the link to Bullseye’s literature on frit tinting.
http://www.bullseyeglass.com/methods-ideas/frit-tinting.html